New Delhi, Aug. 30 -- For around 20 years central bankers have made a virtue of saying more and more about where they think interest rates may be headed. Since becoming chairman of the Federal Reserve in May, Kevin Warsh has made a point of keeping his mouth shut. But on August 28th, at the Fed's annual conference at Jackson Hole, Wyoming, surrounded by the Teton mountains, Mr Warsh had little choice but to talk.

For much of his speech, the Sphinx of the Fed trod familiar ground. Mr Warsh began with what he called a "trail map" for his remarks-careful, he joked, not to call it "forward guidance", the sort of firm statements about the direction of interest rates that he especially dislikes. He explained his fascination with artificial int...